#5 Fix for iperf -d extra connections (bug# 1903811)

[Prashant Patel]

Fix for bug#1903811: "iperf -d creates unnecessary connections from server side"

The fix has added one more bit (a flag indicating "INVALID_DUAL_HDR") in the client header "flags" sent to sever.

When running DUAL mode test:
This bit is clear only for 1 header sent from client iperf instance (needed to run DUAL mode test). For rest of the headers, the INVALID_DUAL_HDR bit is set.
On the iperf server instance, this header bit is used to detect that there is no need to initiate back connection to client side, so from Listener::Run() it will not add another client thread for back connection.

The attached patch is generated against iperf 2.0.4 source code.

[Prashant Patel]

dual mode test fix for extra connections